Re: [Gnu-arch-users] [BUG] feature plan -- version variables

[Aaron Bentley]

Tom Lord wrote:
> Version variables are persistent variables associated 
> with versions.  At each revision within a version, all
> of the variables have a definate value.  By default, 
> each revision inherits the values from its immediate ancestor
> but variable values can be changed by any revision.

Sounds pretty resonable.  I worry a bit because patchlogs are not always 
guaranteed to be present, but maybe I worry too much.

> * Range
>
>   The value of a version variable must be a Pika Scheme s-expression
>   satisfying certain constraints:
>
>         1) Only cons pairs, booleans, small integers,
>            nil, and strings containing only iso-8859-1
>            characters may occur in the value.

Why iso-8859-1?  Since we plan to make patchlogs utf-8, I'd imagine 
limiting it to ASCII until we make patchlogs utf-8.

One thing we could use this for is for version descriptions-- but only 
if people can use their own alphabets for the descriptions.

>         2) Cons pairs may occur in the value only
>            as part of a proper list.
>
>
> * Domain
>
>   The name of a version variable must consist entirely of ascii
>   numbers and letters, dash ('-'), and dot ('.').  
>
>
> * Representation
>
>   Within a project tree, variable values are usually found by
>   reading the patch-log.   The latest patch-log entry for the 
>   tree-version of the project tree may contain a header:
>
>         set-in-version: (<name> <value>)*

Are those parentheses literal charaters or part of the definition 
syntax?  (I'm wondering what the separator is.  Personally, I'd probably 
do it one-var-per-line instead)

Are those map semantics?  I'd imagine if the same name appears multiple 
times, only the last assignment is used?  Or is it an error?

Care to specify a representation for lists, or do you think the list 
user should chooose it?

>   Variables without an explicitly set value have the value false
>   (`#f').
>
>   If the file ./{arch}/++variables exists then it should contain
>   0 or more valid `set-in-version' log message headers -- these
>   override the settings in the latest patch log entry.

Is this file immortal, or is it deleted by commit/import?

>   % tla version-var name value
>   [locally set the value of name to value]
>
>   % tla version-var --unset name
>   [remove any local setting for name]

Would this delete a version-var?
% tla version-var name #f

(Is there any difference between a false value and a missing value?)

Aaron

--
Aaron Bentley
Director of Technology
Panometrics, Inc.